1. Field of the Invention
The present invention relates to lift boats that feature a hull having a plurality of legs, each leg having an associated jacking mechanism that enables the hull to be elevated or lowered relative to the legs and wherein each leg has a load bearing pad that engages the seabed during use. More particularly, the present invention relates to an improved lift boat having an improved leg, hull and pad configuration with improved stability, when jacked up and when underway, featuring port and starboard pads near the bow of the hull that extend laterally of the hull in respective port and starboard directions and that extend into recesses of the hull.
2. General Background of the Invention
Lift boats are well known in the art. These devices (sometimes called jack up barges or jack up rigs) include a floating hull that allows the boat to be transferred from one marine location to another. When the hull reaches a desired location, such as a proposed oil well or other job site, typically three or four legs are lowered from the hull or barge to the sea bed. These legs are then powered downwardly with jacking mechanisms to lift the hull vertically on the legs and above the water's surface. Once in operating position, a jack-up rig presents a stable platform surface for oil and gas well drilling operations, work-over operations, repair or maintenance work etc., notwithstanding the wave action at the water surface below.
There have been many patents that have issued relating to jack-up rigs. An example of a recent patent that discloses a jack-up rig is U.S. Pat. No. 5,139,366 issued to Kenneth Choate and John Laird entitled “OFFSHORE JACK-UP RIG LOCKING APPARATUS AND METHOD”. The Choate et al. patent provides a locking apparatus and method for an offshore jack-up rig having at least one leg extending through the hull and at least one set of rack teeth attached to each of the legs. One or more locking bars are supported from the hull and are movable in a direction substantially normal to the face of the rack teeth. A piston and cylinder power assembly moves the bars towards the teeth and a retention system engages the bars holding them in engagement with the teeth. The elevating system of the rig co-acts with the set bars to lock the hull and legs together.
Another recent patent that relates to jack-up rigs and explains there operation is U.S. Pat. No. 4,813,814 entitled “LEG-HOLDING DEVICE FOR OFFSHORE PLATFORM”.
Other examples of patents that have issued and relate generally to jack-up rigs include U.S. Pat. Nos. 4,722,640; 4,627,768; 4,589,799; 4,505,616; and 4,482,272.
A patent that illustrates the elevating and lowering of a jack-up rig in a marine environment is U.S. Pat. No. 5,224,798, entitled “OVERLOADING DEVICE FOR A JACK-UP OIL PLATFORM AND PLATFORM INCLUDING THE DEVICE” (see FIGS. 4a–f).
A common element of a lift boat is a lifting crane that can be used to lift supplies from its own deck, work boat, supply boat or the like, and place those supplies on the platform. Patents have issued that are directed to the placement of a crane on a jack up barge. Some years ago, a patented crane apparatus was designed to fit over the leg of a smaller sized lift boat wherein the leg was of a cylindrical pipe configuration. U.S. Pat. No. 4,417,664 disclosed generally the concept of mounting a crane having a gantry and a boom about the leg of a lift boat. Another patent that addressed the problem of mounting a crane on a jack-up rig (lift boat) where there is limited space is U.S. Pat. No. 4,652,177. This patent proposes to mount the crane on the jacking structure or jacking tower of the jack-up rig (lift boat).
The following U.S. Patents are incorporated herein by reference: U.S. Pat. Nos. 2,308,743; 3,183,676; 3,290,007; 3,367,119; 3,606,251; 3,750,210; 3,945,450; 3,967,457; 4,417,664; 4,456,404; 4,678,165; 4,813,814; 5,139,366; 5,580,189; 5,797,703; and all patents mentioned herein.